Condensed Answer: An 11-speed chain is narrower than a 9-speed chain and can therefore work with a 9-speed cassette.
The combination, however, makes little financial sense because 11-speed components are more expensive.
In most cases, it’s better to purchase a dedicated 9-speed chain. It’s cheaper and will work out of the box.
Understanding Chain Width and Sprocket Thickness
First, it’s necessary to explain the term cog pitch. The cog pitch is the center-to-center distance between two neighboring cogs on a cassette.
As the number of gears on a cassette increases, the individual sprocket thickness and the cog pitch decrease.
The purpose of this engineering is to preserve the overall width of multi-speed cassettes similar so that they remain compatible with a greater number of freehub bodies.
As a result, 8/9/10 and 11-speed MTB cassettes and hubs are cross-compatible.
The shorter cog pitch, however, makes chains designed for fewer speeds non-compatible with cassettes using more gears than the number that the chain is designed for.
For instance, a 9-speed chain is too thick to be used on an 11-speed cassette. The outer plates will grind against the adjacent cogs.
Below is a table containing the sprocket width and cog pitch of 8,9,10 and 11-speed MTB cassettes:
| Number of Speeds | Cog Pitch | Sprocket Thickness | Chain Outer Width | Inner Chain Width |
| 8 | 4.8mm | 1.85mm | 7.1mm | 2.38mm |
| 9 | 4.35mm | 1.78mm | 6.5 – 6.7mm | 2.18mm |
| 10 | 3.95mm | 1.6mm | 5.84 – 6.1mm | 2.18mm |
| 11 | 3.9mm | 1.6mm | 5.46 – 5.74mm | 2.18mm |
With each gear increase we observe the following:
- The sprockets get thinner.
- The cog pitch gets smaller.
- The outer width of the chain decreases.
Note: A chain has two widths – inner and outer. The inner width is the distance between the inner plates. The inner width doesn’t change much with each gear increase or decrease.
The outer width is the distance between the external plates of the chain. The outer width of the cassette decreases with each gear jump.
This change is necessary to prevent the chain from rubbing against the adjacent cogs and is achieved via thinner outer plates.
For that reason, chains designed for more gears are known to be weaker than chains made for fewer speeds.
The Advantages of Combining an 11-speed Chain With a 9-speed Cassette
- Silent operation
An 11-speed chain is 1.04mm – 0.96mm narrower than an original 9-speed chain. However, the inner width of both chains is the same (2.18mm).
The much narrower profile of 11-speed chains reduces the possibility of chain rubbing and keeps the drivetrain very silent.
- Mud Clearance
The extra space left by an 11-speed chain improves mud clearance.
- More options
If you can’t find a 9-speed chain (unlikely), an 11-speed chain could save the day.
The Downsides of Running an 11-speed Chain On a 9-speed Cassette
- Weaker
9-speed chains are thicker and therefore potentially stronger than 11-speed chains.
- Slow/weird shifting (potentially)
11-speed chains are slimmer than 9-speed chains. Thus, the derailleur has to move ever so slightly more to initiate a shift. In some cases, the delay will result in less than ideal shifting speed.
Whether this problem will manifest depends on the entire drivetrain.
- Subpar Performance At The Front
An 11-speed chain may result in non-optimal shifting between the chainrings. This outcome isn’t certain, however, and its manifestation depends on the entire setup.
- More Expensive
11-speed components tend to be more expensive than 9-speed equivalents. Hence why it makes little financial sense to use an 11-speed chain on a 9-speed drivetrain.
FAQ: Can I use a 9-speed Chain on an 11-speed Cassette?
A 9-speed chain will be too wide for an 11-speed cassette. It will cause rubbing, poor shifting, and premature wear of the drivetrain.
To increase the drivetrain’s lifespan and ensure smooth shifting, it’s recommended to stay away from this combination.
Summary: What You Need To Know
- 11-speed chains have the same inner width as 9-speed chains. Consequently, they have the capacity to engage the sprockets as intended.
- The total/outer width of 11-speed chains is narrower than that of 9-speed chains because the cog pitch of 11-speed cassettes is shorter. (The cog pitch is the center-to-center difference between two cogs on a cassette.)
- An 11-speed chain is expected to make the drivetrain silent, but it can result in less than ideal shifting due to the slack that the derailleur has to compensate for.
- In most cases, it’s better to purchase a dedicated 9-speed chain. It’s cheaper and will work out of the box.
